Researchers have already developed a device that allows you to see through eight-inch-thick concrete walls, but now, scientists have devised another way to reveal objects that are hidden from view: a camera that can see around corners.

Believe it or not, radar systems that can see through walls (aka "wall-through" radar…
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The novel imaging tool works a lot like sonar, which uses echoes to determine the position and shape of distant objects; the difference is that this new technology uses light (and some sophisticated image-processing capabilities) instead of sound.

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Here's how it works. On the left-hand side of this image is a camera. Just right of center is a mannequin, but it's hidden from the camera's view by the wall labeled by the green square; it's your typical blind corner situation.

But there's also a third wall, labeled with a red square. A pulse of light is fired at the third wall, and when it comes into contact with the barrier, the light scatters. A small fraction of that scattered light will collide with the mannequin and scatter again, bounce off the third wall a second time, and find its way back to the camera.

By measuring how long it takes this fraction of scattered light to reach the camera, Ramesh Raska and his colleagues at MIT have managed to reproduce images of hidden objects at very impressive levels of detail. The system's unprecedented accuracy depends on three main factors:

1) The speed and duration of the light pulses. Each pulse lasts just 50 quadrillionths of a second, and each image is constructed from sixty different angles. This is important because some photons will travel the same distance and reach the camera at the same position, even after hitting different parts of the hidden scene. Collecting scattered photons from multiple angles allows the researchers to gain as many perspectives of the hidden scene as possible.

2) The speed of the camera itself. It records an image of the incoming light once every 2 picoseconds; as a result, the camera can resolve structural details of the hidden scene at sub-millimeter resolution.

3) A sophisticated reconstruction algorithm, created by team member Andreas Velten, that makes sense of the various angles recorded by the high-speed camera. Velten is first author on the research paper describing the team's findings, which is published in the latest issue of Nature Communications.

The above video, courtesy of Nature, helps illustrate each of these factors individually. Right now the entire imaging process requires minutes of data crunching, but Raskar and his team are confident that future incarnations of the technology will be able to do this kind of imaging in a matter of seconds. As far as applications are concerned, the team says they envision it being used in pretty much any scenario that requires seeing objects out of your direct line of sight — to peer around a blind intersection, for example, or to spot enemies hiding around a corner.